Moon helps reveal secrets of the Universe

The Moon may be the key to unlocking how the first stars and galaxies shaped the early Universe.

A team of astronomers led by Dr Benjamin McKinley at Curtin University node of the International Centre for Radio Astronomy Research (ICRAR) and the ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D) observed the Moon with a radio telescope to help search for the faint signal from hydrogen atoms in the infant Universe.

“Before there were stars and galaxies, the Universe was pretty much just hydrogen, floating around in space,” Dr McKinley said.

“Since there are no sources of the optical light visible to our eyes, this early stage of the Universe is known as the ‘cosmic dark ages’.

Artist’s impression of a portion in the timeline of the Universe, around the ‘epoch of reionisation’ – the process that ionised most of the material in the cosmos. This is the first moment in the history of the cosmos when matter was in an electrically neutral state (represented in yellow). After that, a few hundred million years passed before these atoms could assemble and eventually give rise to the Universe’s first generation of stars (left of centre, in the illustration). As these first stars came to life, they filled their surroundings with light, which subsequently split neutral atoms apart, turning them back into their constituent particles: electrons and protons. This process, called cosmic reionisation, is shown at the centre of the illustration. The yellow neutral hydrogen gives off a signal that we detect as faint radio waves on Earth. Image credit: ESA – C. Carreau

In research published in the Oxford University Press Monthly Notices of the Royal Astronomical Society today, the astronomers describe how they have used the Murchison Widefield Array (MWA) radio telescope to help search for radio signals given off by the hydrogen atoms.

“If we can detect this radio signal it will tell us whether our theories about the evolution of the Universe are correct.”

Dr McKinley said that in your car radio, you can tune into various channels and the radio waves are converted into sounds.

“Our radio telescope, the Murchison Widefield Array (MWA) in the Western Australian desert, takes the same radio channels and converts the information into images of the sky,” he said.

Dr Benjamin McKinley during a trip to the Murchison Widefield Array telescope in outback Western Australia. The 16 metal ‘spiders’ form a single antenna ‘tile’, of which there are 256, spread out across an area of around 6 km in diameter. Dr McKinley and the team are using this radio telescope to observe the Moon in their search for radio signals from the early Universe.

This radio signal from the early Universe is very weak compared to the extremely bright objects in the foreground, which include accreting black holes in other galaxies and electrons in our own Milky Way.

The key to solving this problem is being able to precisely measure the average brightness of the sky.

However, built-in effects from the instruments and radio frequency interference make it difficult to get accurate observations of this very faint radio signal.

In this work, the astronomers used the Moon as a reference point of known brightness and shape.

Radio waves from our galaxy, the Milky Way, reflecting off the surface of the Moon and observed by the Murchison Widefield Array radio telescope located in outback Western Australia. Credit: Dr Ben McKinley, Curtin University/ICRAR/ASTRO 3D. Moon image courtesy of NASA/GSFC/Arizona State University.

This allowed the team to measure the brightness of the Milky Way at the position of the occulting Moon.

The astronomers also took into account ‘earthshine’—radio waves from Earth that reflect off the Moon and back onto the telescope.

Earthshine corrupts the signal from the Moon and the team had to remove this contamination from their analysis.

With more observations, the astronomers hope to uncover the hydrogen signal and put theoretical models of the Universe to the test.

The Murchison Widefield Array (MWA) is a low-frequency radio telescope and is the first of four Square Kilometre Array (SKA) precursors to be completed.

A consortium of partner institutions from seven countries (Australia, USA, India, New Zealand, Canada, Japan, and China) financed the development, construction, commissioning, and operations of the facility. The MWA consortium is led by Curtin University.

ASTRO 3D

ASTRO 3D is the ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions. It is a collaborative research organisation of six Australian Universities (the Australian National University, Curtin University, the University of Western Australia, Swinburne University of Technology, The University of Melbourne and the University of Sydney) and Australian and international partner institutions.

ICRAR

The International Centre for Radio Astronomy Research (ICRAR) is a joint venture between Curtin University and The University of Western Australia with support and funding from the State Government of Western Australia.